Seriously consider whether you can suffer the loss. First assume you've actually lost everything.
Is it possible to swap the system drive out? That is, could you set that one aside (in a safe or something) so that you could install a different drive to rebuild your system? The reason is, that you might rebuild the system and decide you don't really need the "backup" after all. But if you don't, then you can still attempt recovery.
Really though, assume recovery will cost you a large amount of time and money.
Several times in my life I've been through this, usually due to corrupt backups, or drives that got damaged during backup or restore. I've had to start over from nothing more than once.
I've currently got one system offline for probably ten years that is going to be painful to deal with: my backup is lost and I've got a database that took years to enter by hand. One of these days I need to try to revive that system (Sparcstation 20). That and the hard drives from my Amiga 3000 which unfortunately (drives and backup drives) use a filesystem that only works on hardware I don't really have anymore.